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SNAB
Units 3 and 4 ­ Revision notes

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2.3.1 ­ CELL ORGANELLES (EUKARYOTIC CELL )




Figure 3.8 ­ A 3D animal cell (eukaryotic)

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Organelle Structure and function

Nucleus enclosed in double membrane with pores
contains chromosomes with genes made of DNA to control protein
synthesis


Ribosomes made of RNA and protein
free in cytoplasm or attached to RER
site of protein synthesis


Rough endoplasmic interconnected sacs with ribosomes attached
reticulum transport proteins to…

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2.3.2 ­ PROTEIN SYNTHESIS

Proteins synthesised on the ribosomes of
the RER are moved to other parts of the
cell through the cavities of the
endoplasmic reticulum.

The Golgi apparatus is a stack of
membrane-bound sacs formed from
fused vesicles from the ER.

Proteins are modified here and packaged
in…

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2.3.4 ­ THE CELL CYCLE

Mitosis is a type of cell division, which retains the full or diploid number (2n) of chromosomes.

In humans, a cell with 46 chromosomes divides to form 2 identical daughter cells, each with 46 chromosomes.

Before nuclear division, a copy of each chromosome is made…

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2.3.6 ­ STAGES OF THE CELL CYCLE (MITOSIS)

Cell division is a continuous process, but 4 stages of mitosis (nuclear division) can be described:


Prophase chromosomes condense (get shorter and thicker)
microtubules are organised into a spindle by the centrioles
nuclear membrane breaks down


Metaphase the centromeres of the chromosomes…

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2.3.9 ­ GAMETE PRODUCTION

Gametes are produced in the ovaries and testes of animals by meiosis which:
produces haploid cells (contain half the number of chromosomes found in a body cell: one of each
homologous pair)
creates genetic variation among offspring

During meiosis, pairs of homologous chromosomes line up at…

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2.3.12 ­ GENE TRANSCRIPTION

The specialised function of a cell depends upon the proteins it synthesises ie which genes are expressed.

Transcription of a gene is initiated by RNA polymerase and transcription factors binding to a promoter region
(section of DNA adjacent to gene).


RNA polymerase + transcription factors =…

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Others are influenced by both genotype and environment and show continuous variation eg human height,
skin and hair colour, cancer.


Figure 3.38

A ­ Human blood
groups show
discontinuous
variation.

B ­ Human height
shows continuous
variation.




Human average height has increased in the past 150 years for various reasons.…

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2.3.15 - CANCER

Cancer occurs when the rate of cell multiplication is faster than the rate of cell death.
This causes the growth of a tumour.
Cancer is caused by environmental damage to DNA from
physical factors such as UV light and asbestos
chemical carcinogens such as those in the…

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